[0001] The invention relates to a method and apparatus for monitoring mechanical fiber stress
of optical fiber spans within an optical network, and in particular to a method and
apparatus for predicting an optical fiber cut event.
[0002] An optical network comprises a plurality of network elements connected to each other
via optical links. Each optical link can be composed of one or several optical fiber
spans comprising optical fibers. Optical fiber spans can be subject to mechanical
stress. For instance, due to excavation activities, fibers of one or several fiber
spans within a fiber link connecting two network elements of the network can be stretched
and are at a risk of being cut by mechanical effects. Conventional techniques used
nowadays for predicting fiber cuts are based on monitoring for any degradation in
the bit error rate of a signal received by a receiver and/or a drop in the optical
power of the received signal. However, these conventional techniques are unreliable
in predicting possible fiber cuts and therefore cannot prevent preemptively any traffic
loss in the data network. Conventional techniques may provide unreliable results in
networks where other artifacts, unrelated to a fiber break event, degrade the signal
power or add noise to the channel.
[0003] US 5381005 A discloses an optical fiber stress detector in which the light beam transmitted in
the optical fiber which has to detect stresses is modulated in amplitude by a microwave
alternating signal.
[0005] Accordingly, there is a need for a method and apparatus which allow monitoring of
the mechanical stress experienced by optical fiber spans within an optical network
for the purpose of predicting possible optical fiber cut events.
[0006] The invention provides according to a first aspect a method for monitoring mechanical
fiber stress of optical fiber spans of an optical fiber link within an optical network
comprising
monitoring continuously a timing phase of a received optical signal transported through
an optical fiber link composed of optical fiber spans ;deriving the mechanical fiber
stress in said optical fiber spans of said optical fiber link on the basis of an observed
phase shift of said timing phase within a predetermined observation period of time,
wherein a phase difference of said received optical signal is measured against a fixed
reference signal over a sample interval to provide a phase shift represented by a
time difference between the received optical signal and the reference signal, and
wherein the timing phase of the received optical signal is extracted by a clock recovery
block of a receiver receiving said optical signal transported through the optical
fiber spans of said optical fiber link, wherein a critical mechanical fiber stress
indicating an imminent fiber cut is detected if the observed phase shift of said extracted
timing phase exceeds a first threshold value within the predetermined observation
period of time, and if evaluation of other indicators comprising a bit error rate,
BER, of the received optical signal, a detected chromatic dispersion, a detected polarization
mode dispersion, an optical signal power of the received optical signal, and/or a
polarization dependent loss confirms the imminent fiber cut in the optical fiber spans.
[0007] The invention further provides according to a second aspect an optical network comprising
a plurality of network elements connected to each other via optical links each being
composed of one or more optical fiber spans ;a monitoring unit for continuously monitoring
an extracted timing phase of a received optical signal transported through optical
fiber spans of said optical network; is continuously monitored and a means for measuring
a phase difference of said received optical signal against a fixed reference signal
over a sample interval to provide a phase shift represented by a time difference between
the received optical signal and the reference signal;a calculation unit for deriving
a mechanical fiber stress in said optical fiber spans on the basis of an observed
phase shift of said extracted timing phase within a predetermined observation period
of time; and means for extracting the timing phase of the received optical signal
by a clock recovery block of a receiver receiving said optical signal transported
through the optical fiber spans of said optical fiber link, wherein the calculation
unit is configured to detect a critical mechanical fiber stress indicating an imminent
fiber cut if the observed phase shift of said extracted timing phase exceeds a first
threshold value within the predetermined observation period of time, and if evaluation
of other indicators comprising a bit error rate, BER, of the received optical signal,
a detected chromatic dispersion, a detected polarization mode dispersion, an optical
signal power of the received optical signal, and/or a polarization dependent loss
confirms the imminent fiber cut in the optical fiber spans.
[0008] The invention further provides according to a third aspect an apparatus for monitoring
mechanical fiber stress of optical fiber spans of an optical fiber link within an
optical network said apparatus comprising:a monitoring unit adapted to monitor continuously
a timing phase of a received optical signal transported through said optical fiber
link composed of optical fiber spans ;means for measuring a phase difference of said
received optical signal against a fixed reference signal over a sample interval to
provide a phase shift represented by a time difference between the received optical
signal and the reference signal;a calculation unit adapted to detect a mechanical
fiber stress in said optical fiber spans of said optical fiber link on the basis of
an observed phase shift of the timing phase within a predetermined observation period
of time; and means for extracting the timing phase of the received optical signal
by a clock recovery block of a receiver receiving said optical signal transported
through the optical fiber spans of said optical fiber link, wherein the calculation
unit is configured to detect a critical mechanical fiber stress indicating an imminent
fiber cut if the observed phase shift of said extracted timing phase exceeds a first
threshold value within the predetermined observation period of time, and if evaluation
of other indicators comprising a bit error rate, BER, of the received optical signal,
a detected chromatic dispersion, a detected polarization mode dispersion, an optical
signal power of the received optical signal, and/or a polarization dependent loss
confirms the imminent fiber cut in the optical fiber spans.
[0009] Further advantageous embodiments are described in the dependent claims.
[0010] In the following, possible embodiments of the different aspects of the present invention
are described in more detail with reference to the enclosed figures.
- Fig. 1
- shows a diagram of an exemplary embodiment of an optical network according to the
present invention;
- Fig. 2
- shows a block diagram of a possible embodiment of an apparatus for monitoring mechanical
fiber stress of optical fiber spans within an optical network according to an aspect
of the present invention;
- Fig. 3
- shows a diagram of an exemplary implementation of a fiber link between two optical
network elements to illustrate a possible embodiment of the method and apparatus according
to the present invention;
- Fig. 4A, 4B
- show a diagram for illustrating the expansion of an optical fiber due to mechanical
stress to illustrate the operation of the method and apparatus according to the present
invention;
- Fig. 5
- shows a block diagram of a possible embodiment of a receiver as employed within a
network according to the present invention;
- Fig. 6
- shows a block diagram of a circuit for illustrating a possible embodiment of the method
and apparatus according to the present invention;
- Fig. 7
- shows signal diagrams for illustrating an operation of the circuit shown in Fig. 6;
- Fig. 8A, 8B, 8C
- show exemplary diagrams of fiber cut incidents in the field for illustrating the operation
of the method and apparatus according to the present invention;
- Fig. 9
- shows a diagram for illustrating fiber failure probability as a function of an applied
mechanical stress to illustrate the operation of the method and apparatus according
to the present invention; and
- Fig. 10
- shows a flowchart of a possible embodiment of the method according to the present
invention.
[0011] Fig. 1 shows an exemplary embodiment of an optical network 1 according to the present
invention. The optical network 1 comprises a plurality of network elements connected
to each other via optical links each being composed of one or more optical fiber spans.
In the shown simple exemplary embodiment of the optical network 1, the network comprises
network elements A, B, C, D, E, F. The optical network elements A to F can be formed
by interfaces to routers, and are therefore the only locations in the optical network
1 where an optical signal can be either generated or terminated. The network elements
A to F are connected together through optical fiber links which are composed of one
or more optical fiber spans with or without amplification. For instance, network element
A is connected to the network element B via an optical fiber link AB. The link is
composed of one or several optical fiber spans, wherein after each of the spans the
optical signal is regenerated either optically or electronically. The set of optical
links that does connect an ingress network element and an egress network element in
the optical network 1 forms a signal path. For instance, in the optical network 1
as shown in Fig. 1, there is a signal path ABC connecting network elements A and C.
Such a working signal path connects an ingress network element such as network element
A with an egress network element such as network element C. For every working signal
path, a corresponding protection signal path can be provided. This protection signal
path is partially or completely disjoint from the working signal path to be protected
and shares the same ingress and egress points. In the example shown in Fig. 1, the
protection signal path ADEFC is provided to protect the working signal path ABC.
[0012] In the optical network 1 according to the present invention as illustrated in Fig.
1, an extracted timing phase of a received optical signal transported through optical
fiber spans of said optical network 1 is continuously monitored and a mechanical stress
in said optical fiber spans is derived on the basis of an observed phase shift of
the extracted timing phase within a predetermined observation period of time. Optical
links do comprise optical fiber spans connected to each other in series via optical
amplifiers OA as shown in Fig. 1. In a further embodiment, the monitored optical signal
is an optical signal which is transported through said optical fiber spans in a wavelength
division multiplexing, WDM, channel. In an alternative embodiment of the optical network
1 according to the present invention, the monitored optical signal can also be a specific
optical signal transported through said optical fiber spans in an optical supervisory
channel, OSC, and can comprise a predetermined monitor wavelength. Although none of
the regeneration nodes along the link can form an ingress or egress point, a supervisory
optical channel, OSC, can be optionally generated and terminated at these regeneration
nodes or amplifiers. Optical signals can co-propagate together with the signals in
the optical channels in the supervisory optical channels, OSC, within the same other
fiber span and they can be responsible for the communication between the different
network nodes and optionally for monitoring the performance of each individual optical
fiber span.
[0013] In a possible embodiment, a critical mechanical fiber stress indicating an imminent
fiber cut of an optical fiber within an optical fiber span can be detected, if the
observed phase shift of the extracted timing phase exceeds a first threshold value,
TH1, within a predetermined observation period of time. In a possible implementation,
the first threshold value, TH1, is adjustable. Further, in a possible implementation,
the predetermined observation period can also be adjustable. In a possible embodiment,
the timing phase of the received optical signal can be extracted by a clock recovery
block of a receiver of the network element receiving the optical signal transported
through the optical fiber spans. If an observed phase shift of the timing phase within
the observation period of time exceeds the first threshold value, TH1, then other
indicators are evaluated in a possible embodiment to confirm an imminent fiber cut
in the optical fiber spans. These other indicators can comprise in a possible embodiment
a bit error rate, BER, of the received optical signal, a detected chromatic dispersion,
a detected polarization mode dispersion, an optical signal power of the received optical
signal, and/or a polarization dependent loss.
[0014] In a possible embodiment of the optical network 1 as illustrated in Fig. 1, if a
critical mechanical stress in one of the optical fiber spans of a link between two
network elements of the optical network 1 is detected, a control plane, CP, is notified
by the respective receiver to switch data traffic away from the affected path comprising
the optical link with the affected optical fiber span to a protection signal path.
Alternatively, the receiver can notify the control plane, CP, to perform a shutdown
of the affected signal path comprising the at least one optical link with the affected
optical fiber span. For instance, if a receiver in network element B of the optical
network 1 as illustrated in Fig. 1 detects a critical mechanical stress in one of
the optical fiber spans of the link AB connecting the network element A and B of the
optical network 1, the receiver of network element B can in a possible exemplary embodiment
notify the control plane, CP, of the network 1 about the detected critical mechanical
stress. The control plane, CP, can then either switch data traffic away from the affected
signal path, SP, to a protection signal path, PSP, or perform a shutdown of the affected
signal path, SP. For instance, the control plane, CP, can in the given example switch
data traffic away from the affected signal path ABC comprising the optical link with
the affected optical fiber span to the protection signal path ADEFC. Alternatively,
the control plane, CP, can shutdown the affected signal path ABC comprising the optical
link with the affected optical fiber span. If an imminent fiber cut of an optical
fiber span is detected, the control plane, CP, can be notified by the respective receiver
and switch data traffic away from the affected signal path comprising the respective
optical fiber span to a protection signal path, PSP. In a possible embodiment, a critical
mechanical stress in the affected optical fiber span of an optical link between two
network elements of the optical network 1 is detected, if an observed phase shift
is equivalent to a delay of several data symbols within a predetermined time period.
In a possible embodiment, the timing phase of the received optical signal is continuously
monitored and observed changes to the phases are reported to derive the mechanical
stress in the optical fiber spans on the basis of the observed phase shift.
[0015] In a further possible embodiment, the phase difference of the received optical signal
is measured against a fixed reference signal over a sample interval to provide a phase
shift represented by a time difference between the received optical signal and the
reference signal. In a possible implementation, the error signal can be represented
as a time difference between the reference and the incoming signal and may be accumulated
over multiple sample intervals to determine a threshold of fiber overstress conditions.
In a possible embodiment, an optical signal is monitored that is transported through
the optical fiber spans in a wavelength division multiplexing, WDM, channel. In an
alternative embodiment, an optical signal is monitored which is transported through
the optical fiber spans in an optical supervisory channel, OSC, and comprises a predetermined
monitor wavelength.
[0016] In a further possible embodiment, instances of the monitored mechanical fiber stress
for different optical fiber spans are recorded and evaluated to localize an affected
optical fiber span of an optical link between network elements of the optical network
1. In a possible embodiment, the instances of the monitored mechanical fiber stress
are recorded only, if the observed phase shift of the extracted timing phase within
the predetermined observation period of time exceeds a second threshold value, TH2.
The second threshold value, TH2, can also be adjustable. In a possible embodiment,
the first and second threshold values TH1, TH2 are adjusted by the control plane,
CP, of the network 1.
[0017] Fig. 2 shows a block diagram of a possible embodiment of an apparatus 2 for monitoring
mechanical fiber stress of optical fiber spans within an optical network 1 according
to the present invention. As can be seen in Fig. 2, the apparatus 2 comprises a monitoring
unit 2a and a calculation unit 2b. The monitoring unit 2a is adapted to monitor continuously
a timing phase of a received optical signal transported through said optical fiber
spans. The calculation unit 2b is adapted to detect a mechanical fiber stress in the
optical fiber spans on the basis of an observed phase shift of the timing phase within
a predetermined observation period of time. The monitoring apparatus 2 can be integrated
in a receiver of a data network element such as data network elements A to F in the
optical network 1 as illustrated in Fig. 1. In a further possible embodiment, the
apparatus 2 can be formed by a separate unit which can be connected to a data network
element such as data network elements A to F of the network 1. For instance, the apparatus
2 can be connected at the receiving side of a data network element such as data network
element B for monitoring an optical signal received from another network element such
as network element A via a link such as link AB. In a possible embodiment, the calculation
unit 2b can also evaluate the detected mechanical fiber stress and notify a control
plane, CP, if the detected mechanical fiber stress is critical. In a possible embodiment,
the calculation unit 2b detects a critical mechanical fiber stress indicating an imminent
fiber cut, if the observed phase shift of the extracted timing phase exceeds a first
threshold value, TH1, within a predetermined observation period. In a further possible
implementation, the calculation unit 2b can evaluate other indicators to confirm an
imminent fiber cut in the optical fiber spans, if an observed phase shift of the timing
phase within the predetermined observation period exceeds this first threshold value,
TH1. In a possible embodiment, the calculation unit 2b can notify the control plane,
CP, if a critical mechanical stress of one of the optical fiber spans of an optical
link between two network elements of the optical network 1 is detected. In a possible
embodiment, instances of the monitored mechanical fiber stress for different optical
fiber spans are received and evaluated by the calculation unit 2b to localize an affected
optical fiber span of an optical link between network elements of the optical network
1. In a possible embodiment, instances of the monitored mechanical fiber stress are
recorded and memorized in a memory unit of the apparatus 2. In a possible implementation,
the instances are only recorded, if the observed phase shift of the timing phase within
the predetermined observation period exceeds a second threshold value, TH2. In a possible
embodiment, the apparatus 2 as illustrated in Fig. 2 comprises an interface for adjusting
a first and/or a second threshold value.
[0018] Fig. 3 shows a diagram for illustrating a possible embodiment of the method and apparatus
according to the present invention. Fig. 3 shows a fiber link between two network
elements, A, B, of an optical network 1. In the shown exemplary embodiment, the first
network element A forms an ingress node and network element B forms an egress node
connected to each other via an optical link, OL, comprising several optical fiber
spans. The optical link is composed of several optical fiber spans, FS1, FS2, FS3,
FS4, connected to each other in series via optical amplifiers, OA1, OA2, OA3.
[0019] In the shown example of Fig. 3, the optical signal path, SP, comprises a single optical
link, OL, connecting network element A and network element B. The optical link comprises
four fiber spans FS1, FS2, FS3, FS4 connected to each other via optical amplifiers
OA1, OA2, OA3. In the embodiment illustrated in Fig. 3, phase delays caused by mechanical
fiber stress can be detected by the use of an optical supervisory channel, OSC. In
this embodiment, the optical signal monitored by the monitoring unit 2a of the apparatus
2 is transported through fiber spans FSi in an optical supervisory channel, OSC, and
does comprise a predetermined monitor wavelength. In the embodiment of Fig. 3, the
signal transported in the optical supervisory channel, OSC, comprising a predetermined
monitoring wavelength with appropriate modulation is generated at each amplifier,
OA, and at each network element AB and is transmitted over single fiber spans to the
neighboring amplifier or network element. By monitoring the mechanical fiber stress
for each individual fiber span, FS, and recording the instances when a predetermined
delay threshold has been reached (thus indicating a critical mechanical fiber stress)
on a span-by-span basis allows a network operator to determine which fiber span, FS,
of the optical link, OL, connecting network elements A, B is causing a degradation
in transmission performance of the WDM system. For instance, if such events or situations
with critical mechanical fiber stress occur repeatedly, the operator of the network
is able to localize a fault of a specific fiber span FS and can act before the fiber
stress leads to a fiber cut. Fig. 3 shows an exemplary embodiment specific to OSC.
Other embodiments are possible. With the method according to the present invention
any signal other than the WDM channels or the OSC channel can be used. The only requirement
for the signal is to be time modulated in order for the receiver to be able to detect
the shift of its phase. For instance it is possible to use a separate wavelength which
is not necessarily the same one used for OSC, the separate wavelength signal can be
implemented with optimized modulations for improved resolutions or accuracy for phase
measurement for fiber stress detection.
[0020] As shown in Fig. 3, a mechanical disturber, MD, exerts mechanical stress on the fibers
of fiber span FS3. Each optical amplifier, OAi, in the optical supervisory channel,
OSC, can be dropped and added as illustrated in Fig. 3. The mechanical stress caused
by the mechanical disturber, MD, leads to a critical fiber stress or event which can
be recorded in a logfile of an apparatus 2 according to the present invention. A mechanical
stress of an optical fiber span, FS, can be detected at a receiver. In a possible
embodiment, the receiver is located at a data network element such as data network
element B illustrated in Fig. 3. This receiver comprises an apparatus 2 for monitoring
mechanical fiber stress as illustrated in Fig. 2. In a further possible embodiment,
the apparatus 2 for monitoring a mechanical fiber stress according to the present
invention as illustrated in Fig. 2 can also be connected to one or several optical
amplifiers OA
i to monitor an optical supervisory channel, OSC. In a still further possible embodiment,
the apparatus 2 for monitoring mechanical fiber stress of optical fiber spans within
an optical network 1 can also be integrated in one or several optical amplifiers,
OAi, of an optical fiber link, OL, connecting two data network elements, A, B, of
the optical networks. Alternatively, the apparatus 2 is integrated at the receiving
side, for instance in data network element B as illustrated in Fig. 3 and adapted
to evaluate one or several optical supervisory channels, OSC
i. In an alternative embodiment, the optical signal monitored by the receiver of apparatus
2 according to the present invention is not transported in an optical supervisory
channel, OSC, but in a conventional wavelength division multiplexing channel, WDM.
If the monitored mechanical fiber stress becomes critical indicating a possible fiber
cut, the control plane, CP, of the optical network 1 can be notified by the receiver
and switch data traffic away from the detected signal path, SP, comprising the optical
link, OL, with the affected optical fiber span, FS, to a protection signal path, PSP.
The result of this fast switching is a lower amount of data loss as a result of a
fiber cut if it happens. In a still further possible embodiment, if a critical mechanical
stress indicating an imminent fiber cut is detected, the control plane, CP, of the
optical network 1 can take actions to avoid the effects of the imminent fiber cut.
The method which is provided to detect a fiber cut can also be used to detect an abnormal
mechanical stress which could adversely affect the transmission performance of the
WDM system, potentially leading to a fiber cut in the future. In a possible embodiment,
several instances of mechanical fiber stress are recorded which subsequently are evaluated
to address the root cause of the fiber stress events.
[0021] In a first step S1, the timing phase of a received optical signal transported through
optical fiber spans is monitored continuously. In a further step S2, a mechanical
fiber stress in the optical fiber spans is derived or calculated on the basis of an
observed phase shift of the timing phase within a predetermined observation period
of time.
[0022] In a possible embodiment, the apparatus 2 for monitoring mechanical fiber stress
according to the present invention as shown in Fig. 2 can be integrated in an optical
coherent receiver as illustrated in Fig. 5. The receiver 5 comprises a clock recovery
block receiving optical signals transported through optical fiber spans. The timing
phase of the received optical signal is extracted by the clock recovery block of the
receiver. The monitoring unit 2a integrated in the receiver as shown in Fig. 5 is
adapted to monitor continuously the timing phase of the received optical signal. The
monitoring unit 2a continuously monitors a gradual phase shift that is equivalent
to a delay in the order of several symbols taking place in a period of time that can
be in a possible implementation less than 500msec which is a typical duration of a
fiber cut incident or fiber cut event. The number of the symbols does depend on the
Baud rate of the received optical signal. In case that a phase shift is encountered,
the calculation unit 2b can make the conclusion that there is a fiber cut incident
which can be optionally further confirmed by evaluating further indicators including
chromatic dispersion, polarization mode dispersion, bit error rate, BER, of the received
optical signal, the optical signal power of the received optical signal signal to
noise ratio, the phase shift of other WDM channels sharing the same path or a polarization
dependent loss. Once the calculation unit 2b of the apparatus 2 integrated in the
receiver has confirmed that a fiber cut incident is in progress, it can request a
control plane, CP, of the optical network 1 to take actions that does guarantee that
the data traffic is switched away from that particular optical link, OL, without losing
any data packets. The control plane, CP, of the optical network 1 can chose any strategy
in this case for switching the data traffic away from the affected optical link, OL.
In a possible embodiment, the control plane, CP, can use the OSPF-TE protocol to perform
a graceful shutdown of the affected signal path, SP, where the signal path, SP, will
be announced to have a zero bandwidth in order to guarantee that no new LSPs are established.
Afterwards, the control plane, CP, can request the existing LSPs on that signal route
to move to a different signal path. Alternatively, the control plane, CP, of the network
1 can switch the data traffic to a protection signal path, PSP, in case of 1+1 or
1:N protection, if the start-up time for that signal path is sufficiently short.
[0023] The clock recovery block of the receiver illustrated in Fig. 5 is provided to extract
a timing phase of the received optical signal in order to resample the signal at the
correct sampling instances. Regardless of the algorithm employed in the clock recovery
block, the phase value delivered by this clock recovery block can be used to measure
a delay to the received optical signal that is caused by mechanical tension on a transmission
optical fiber. The amount of delay is directly proportional to the level of tension
taking place on the optical fiber or fiber span, FS, and therefore its quantity can
be used to discover the fiber links that are at a high risk of being cut.
[0024] In a possible embodiment, the timing phase of the received optical signal is continuously
monitored and observed changes to the phases are reported to derive the mechanical
stress in the optical fiber spans, FS, on the basis of the observed phase shift. Alternatively,
a phase difference of the received optical signal is measured against a fixed reference
signal over a sample interval to provide a phase shift represented by a time difference
between the received optical signal and the reference signal.
[0025] Fig. 6 shows a block diagram of a phase locked loop, PLL, which can be used to monitor
a phase offset of an incoming optical signal. In the embodiment shown in Fig. 6, the
recovered signal rec(t) is applied to a phase detector, PD. The time constant of a
following loop filter, LF, is established to hold a phase of a reference signal ref(t)
for at least twice the desired measurement period of the break detection interval.
[0026] Fig. 7 shows signal diagrams of the recovered signal and the reference signals as
well as an error signal, e(t), output by the phase detector, PD. As this phase of
the recovered optical signal rec(t) begins to shift during a fiber mechanical stress
event, the signal phase of the reference signal ref(t) is maintained over the measurement
interval resulting in an error signal e(t) that represents the phase shift of the
recovered signal rec(t). The error signal e(t) can also be represented as a voltage
that can be used as a threshold monitored to detect a pending cut or break event.
[0027] An ideal error signal e(t) can be represented as follows:
where
and
f
n is the nominal rate of the signal.
[0028] In an alternative implementation of measuring the phase offset, a time interval error
signal, x(t), is defined as follows:
[0029] In this implementation, the phase difference is measured against a fixed reference
signal over a sample interval lasting for example 1ms. The error signal is represented
as a time difference between the reference and the incoming reception signal and can
be accumulated over multiple sample intervals to determine a threshold for fiber overstress
conditions.
[0030] The method according to the present invention is also suitable for constant monitoring
of a system performance, wherein a maximum deviation of time error is recorded over
longer performance monitoring periods thereby reporting the long-term health of the
respective transmission medium.
[0031] The optical fiber communication of the optical network 1 as illustrated in Fig. 1
is based on transmitting optical signals through fiber spans of above ground or underground-buried
optical fibers. These optical fiber links, OL, of the optical network can run through
different geographical areas and consequently they are often subject to mechanical
disturbances that, in some cases, can be very aggressive, and which might even lead
to a fiber cut. For example, excavation activities over a buried optical fiber cable
can lead to a fiber cut of the respective optical fiber link, OL.
[0032] Figs. 8A, 8B, 8C show examples for fiber cut events in the field. As can be seen,
a fiber cut process can be relatively fast and on average takes a time between lOOps
and 500ms. Figs. 8A, 8B, 8C plot the optical power of the received optical signal
as a function of time. In case of a fiber cut, all of the optical channels carried
on the respective fiber cable are interrupted which represents a worst-case scenario
for a telecommunication service provider who is obliged to provide highly reliable
communication channels for his customers. With the method and apparatus according
to the present invention it is possible for the service provider to monitor the optical
transmission links. With the method and apparatus according to the present invention,
parameters reported by an optical receiver are evaluated to indicate a level of mechanical
tension or stress on an optical fiber and to subsequently predict optical links, OLs,
that are at a high risk of being cut. A fast and reliable mechanism to alert a fiber
cut in progress can be used by the network management software of the service provider
to switch the data traffic channels being at risk of being cut to an alternative route
or protection signal path, PSP, before rather than after the fiber cut has occurred.
Accordingly, with the method and apparatus according to the present invention, a preemptive
switching can reduce or eliminate a data loss caused by a fiber cut when compared
to a conventional procedure currently in use.
[0033] Figs. 4A, 4B show a diagram for illustrating the expansion of an optical fiber due
to mechanical stress caused by a mechanical disturber, MD. As can be seen in Fig.
9B, the mechanical tension increases the propagation time of the optical signal transmitted
through the optical fiber. Fig. 9A illustrates an optical fiber without any mechanical
stress. Fig. 9B shows a mechanical fiber subject to mechanical stress.
[0034] The travelling time of a signal transmitted through the optical fiber without stress
is:
wherein L is the length of the fiber.
[0035] The travelling time of the signal in the optical fiber subject to mechanical stress
is:
wherein L represents the length of the fiber without mechanical stress and Δ
L is the additional length caused by the mechanical stress.
[0036] For a conventional optical telecommunication fiber, roughly a strain of 1% is caused
by a load of 100kpsi (kilo pound per square inch). If an optical fiber with a length
L is strained by 1%, its length increases by 1% and so does the signal transmission
time.
[0037] Fig. 9 illustrates a diagram showing a failure probability of an optical fiber as
known to a person skilled in the art and published in "
Specialty optical fibers handbook", Academic Press, 2011, p 751, Méndez, Alexis, and
Ted F. Morse. As can be seen, the failure probability of an optical fiber is below 1% for any
tension level that is below 500kpsi. Accordingly, a fiber section of an optical fiber
with a length L must expand roughly by 5% before breaking down. For example, if a
one meter section of a buried optical fiber has experienced a tension of 500kpsi,
its length, L, will be increased by around 5cm. For instance, for a 120Gb/sec DP-QPSK
signal having a Baud rate of about 30GBaud, this translates into a time delay of approximately
7.5 symbols taking place within a time period of less than 500ms. This time delay
can be observed by the apparatus 2 according to the present invention.
[0038] A force of 100kpsi applied to a certain optical fiber results in a strain of 1%.
The relationship between strain and the strength of the force applied to the fiber
is almost linear and can be represented as:
[0039] The length, L, of an optical fiber subject to an X% strain increases by X%*L, wherein
L is the length of the fiber section that is under tension. Consequently, the relationship
between the stretch of fiber length and the level of applied mechanical strength is
linear as well and can be written as:
[0040] This linear relationship is maintained until the strength level is in excess of 500kpsi,
where the probability of a fiber to break increases significantly.
[0041] For example, if a 1m section of a certain optical fiber is subject to a force of
300kpsi (strain = 3%), its length, L, is increased by: 1 x 300 x 10
-4 = 0.03[m]. Since the speed of light in an optical fiber is approximately
c/1.48=2.02x10
8m/s,
wherein c is the speed of light in vacuum, the signal propagating through the fiber
section does experience an extra delay of Δτ = 0.03[m]/2.02x10
8[m/s] = 148ps.
[0042] Similarly, for example, if an optical signal is delayed by approximately 200ps, the
receiver can interpret that a 400kpsi strength has been applied to the 1m optical
fiber section.
[0043] If the strength level increases to about 500kpsi, the probability of breaking the
fiber does increase significantly as shown in Fig. 9. Therefore, if the receiver measures
a delay Δτ = 250ps, it can detect that the 1m optical fiber section under tension
is about to break. Other parameters can be used as well to measure the amount of delay
of the signal at the receiver side. For instance, for a 30GBaud optical signal, a
delay Δτ = 250ps is equivalent to a phase shift of 46.5 radians or a shift of 7.5
symbols.
[0044] The delay (Δτ) is a function of the length L of the fiber section under tension.
Since typical values for the length L are in the order of few meters in the case of
having an excavation activity on the fiber, the receiver is adapted to set a certain
threshold, TH, on the signal delay (or similarly, the phase shift) that can be used
to predict an imminent fiber cut. This threshold, TH, can be crossed within a time
interval of ≤200ms, which is typically the maximum duration for a fiber cut incident.
[0045] Fig. 10 shows a flowchart of a possible exemplary embodiment of the method according
to the present invention. In a first step, Sa, the phase of this received signal is
recovered in the clock recovery block of the receiver. Then, in a further step Sb,
a gradual phase shift that is equivalent to multiples of the symbol duration (which
depends on the Baud rate) taking place over a period of time that is less than 500ms
is inspected.
[0046] If a large phase shift is encountered in step Sc, this is interpreted as having a
fiber cut in progress.
[0047] In a further optional step Sd, the apparatus looks for other indicators to consolidate
the conclusion on the incident fiber cut. These additional indicators which are evaluated
to consolidate that the expected imminent fiber cut can comprise a bit error rate,
BER, SNR, or the phase shift of other WDM channel sharing the same path of the received
optical signal, a chromatic dispersion, a polarization mode dispersion, the optical
signal power of the received optical signal and a polarization dependent loss.
[0048] In a further step Se, it is confirmed to the control plane software of the network
1 that a current signal path, SP, will probably be lost. The control plane, CP, is
provided to guarantee that there are no packet losses. Accordingly, in a further step,
the control plane, CP, can either perform a graceful signal path shutdown (step Sf)
or switch data traffic to a protection signal path, PSP, of the network 1 (step Sg)
.
[0049] The idea underlying the method and apparatus according to the present invention is
based on the fact that the length, L, of the optical fiber section under tension expands
by a certain amount that is proportional to the level of tension applied to it. The
optical receiver can perform a DSP algorithm to the received signal. The method according
to the present invention can be implemented in any optical receiver type, for instance
in an optical coherent receiver. Monitoring the variations in the phase of the arriving
signal using the information of the clock recovery block allows to discover a fiber
that is subject to a certain level of mechanical tension. With the method and apparatus
according to the present invention it is possible to protect optical communication
channels against failures in an optical transmission fiber that are caused by any
kind of mechanical disturbances. With the method and apparatus according to the present
invention, it is possible to discover fiber links that are about to be cut, for example
due to excavation activities and to send a corresponding message or notification.
This message or notification can be sent for example to a control plane, CP, of the
network 1 in order to reroute the optical channels to different optical links, OL.
[0050] The method and apparatus according to the present invention allow a simple implementation
requiring no extra software blocks or complicated DSP algorithms. Further, the method
according to the present invention is generic to any optical signal and any link type,
i.e. aerial or buried and any receiver type and any signal type as long as it is time
modulated. With the method and apparatus according to the present invention it is
possible to detect an optical fiber cut and to start the channel restoration process
even before having any degradation of the signal quality, e.g. increased BER. This
capability is very significant for modern high-capacity optical links, OLS, where
BER margins are reduced significantly in order to compensate for higher OSNR requirements
(OSNR: Optical Signal to Noise Ratio) of the high-speed optical signals.
1. A method for monitoring mechanical fiber stress of optical fiber spans (FS) of an
optical fiber link within an optical network (1) comprising:
monitoring continuously a timing phase of a received optical signal transported through
an optical fiber link (OL) composed of optical fiber spans (FS);
deriving the mechanical fiber stress in said optical fiber spans (FS) of said optical
fiber link (OL) on the basis of an observed phase shift of said timing phase within
a predetermined observation period of time, wherein a phase difference of said received
optical signal is measured against a fixed reference signal over a sample interval
to provide a phase shift represented by a time difference between the received optical
signal and the reference signal, and wherein the timing phase of the received optical
signal is extracted by a clock recovery block of a receiver receiving said optical
signal transported through the optical fiber spans (FS) of said optical fiber link
(OL), wherein a critical mechanical fiber stress indicating an imminent fiber cut
is detected if the observed phase shift of said extracted timing phase exceeds a first
threshold value within the predetermined observation period of time, and if evaluation
of other indicators comprising a bit error rate, BER, of the received optical signal,
a detected chromatic dispersion, a detected polarization mode dispersion, an optical
signal power of the received optical signal, and/or a polarization dependent loss
confirms the imminent fiber cut in the optical fiber spans (FS).
2. The method according to claim 1,
wherein if a critical mechanical stress in one of the optical fiber spans (FS) of
said optical fiber link (OL) between two network elements of said optical network
(1) is detected a message or notification is sent by said receiver to switch data
traffic away from the affected path comprising the optical fiber link (OL) with the
affected optical fiber span (FS) to a protection signal path or to perform a shutdown
of the affected signal path comprising the optical fiber link (OL) with the affected
optical fiber span (FS).
3. The method according to claim 1,
wherein a critical mechanical stress in the affected optical fiber span (FS) of an
optical fiber link (OL) between two network elements of said optical network (1) is
detected if an observed phase shift is equivalent to a delay of several data symbols
within a predetermined period.
4. The method according to one of the preceding claims 1 to 3,
wherein the optical signal is transported through said optical fiber spans (FS) in
a wavelength division multiplexing, WDM, channel.
5. The method according to one of the preceding claims 1 to 3,
wherein the optical signal is transported through said optical fiber spans (FS) in
an optical supervisory channel, OSC, and comprises a predetermined monitor wavelength.
6. The method according to one of the preceding claims 1 to 5,
wherein instances of the monitored mechanical fiber stress for different optical fiber
spans (FS) are recorded and evaluated to identify an affected optical fiber span (FS)
of said optical fiber link (OL) between network elements of said optical network (1).
7. The method according to claim 6,
wherein the instances of the monitored mechanical fiber stress are recorded if the
observed phase shift of the extracted timing phase within the predetermined observation
period of time exceeds a second threshold value.
8. The method according to one of the preceding claims 1 to 7,
wherein the timing phase of said received optical signal is continuously monitored
and observed changes to the phases are reported to derive the mechanical fiber stress
in the optical fiber spans (FS) of said optical fiber link (OL) on the basis of the
observed phase shift.
9. An optical network (1) comprising
a plurality of network elements (A-F) connected to each other via optical links (OL)
each being composed of one or more optical fiber spans (FS);
a monitoring unit (2A) for continuously monitoring an extracted timing phase of a
received optical signal transported through optical fiber spans (FS) of said optical
network (1); and
means for measuring a phase difference of said received optical signal against a fixed
reference signal over a sample interval to provide a phase shift represented by a
time difference between the received optical signal and the reference signal;
a calculation unit (2B) for deriving a mechanical fiber stress in said optical fiber
spans (FS) on the basis of an observed phase shift of said extracted timing phase
within a predetermined observation period of time; and means for extracting the timing
phase of the received optical signal by a clock recovery block of a receiver receiving
said optical signal transported through the optical fiber spans (FS) of said optical
fiber link (OL), wherein the calculation unit (2b) is configured to detect a critical
mechanical fiber stress indicating an imminent fiber cut if the observed phase shift
of said extracted timing phase exceeds a first threshold value within the predetermined
observation period of time, and if evaluation of other indicators comprising a bit
error rate, BER, of the received optical signal, a detected chromatic dispersion,
a detected polarization mode dispersion, an optical signal power of the received optical
signal, and/or a polarization dependent loss confirms the imminent fiber cut in the
optical fiber spans (FS).
10. The optical network according to claim 9,
wherein the optical links (OL) comprise optical fiber spans (FS) connected to each
other in series via optical amplifiers (OA).
11. The optical network according to claim 9 or 10,
wherein the monitored optical signal is an optical signal which is transported through
said optical fiber spans (FS) in a wavelength division multiplex, WDM, channel or
wherein the monitored optical signal is a specific optical signal transported through
said optical fiber spans (FS) in an optical supervisory channel, OSC, and comprises
a predetermined monitor wavelength.
12. An apparatus for monitoring mechanical fiber stress of optical fiber spans (FS) of
an optical fiber link (OL) within an optical network (1) said apparatus comprising:
a monitoring unit (2A) adapted to monitor continuously a timing phase of a received
optical signal transported through said optical fiber link (OL) composed of optical
fiber spans (FS);
means for measuring a phase difference of said received optical signal against a fixed
reference signal over a sample interval to provide a phase shift represented by a
time difference between the received optical signal and the reference signal;
a calculation unit (2B) adapted to detect a mechanical fiber stress in said optical
fiber spans (FS) of said optical fiber link (OL) on the basis of an observed phase
shift of the timing phase within a predetermined observation period of time; and
means for extracting the timing phase of the received optical signal by a clock recovery
block of a receiver receiving said optical signal transported through the optical
fiber spans (FS) of said optical fiber link (OL), wherein the calculation unit (2b)
is configured to detect a critical mechanical fiber stress indicating an imminent
fiber cut if the observed phase shift of said extracted timing phase exceeds a first
threshold value within the predetermined observation period of time, and if evaluation
of other indicators comprising a bit error rate, BER, of the received optical signal,
a detected chromatic dispersion, a detected polarization mode dispersion, an optical
signal power of the received optical signal, and/or a polarization dependent loss
confirms the imminent fiber cut in the optical fiber spans (FS).
1. Verfahren zum Überwachen einer mechanischen Faserbelastung von Lichtleitfaserstrecken
(Fibre Spans, FS) eines Lichtleitfaserlinks innerhalb eines optischen Netzwerks (1),
wobei das Verfahren Folgendes umfasst:
kontinuierliches Überwachen einer Zeitsteuerungsphase eines empfangenen optischen
Signals, das durch einen Lichtleitfaserlink (Optical Fibre Link, OL) transportiert
wird, der aus Lichtleitfaserstrecken (FS) zusammengesetzt ist;
Ableiten der mechanischen Faserbelastung in den Lichtleitfaserstrecken (FS) des Lichtleitfaserlinks
(OL) auf der Basis einer beobachteten Phasenverschiebung der Zeitsteuerungsphase innerhalb
eines vorgegebenen Beobachtungszeitraums, wobei eine Phasendifferenz des empfangenen
optischen Signals anhand eines festen Referenzsignals über ein Abtastintervall gemessen
wird, um eine Phasenverschiebung bereitzustellen, die durch eine Zeitdifferenz zwischen
dem empfangenen optischen Signal und dem Referenzsignal repräsentiert wird, und wobei
die Zeitsteuerungsphase des empfangenen optischen Signals durch einen Taktwiederherstellungsblock
eines Empfängers extrahiert wird, der das optische Signal empfängt, das durch die
Lichtleitfaserstrecken (FS) des Lichtleitfaserlinks (OL) transportiert wird, wobei
eine kritische mechanische Faserbelastung, die eine unmittelbar bevorstehende Faserdurchtrennung
anzeigt, detektiert wird, wenn die beobachtete Phasenverschiebung der extrahierten
Zeitsteuerungsphase einen ersten Schwellenwert innerhalb des vorgegebenen Beobachtungszeitraums
übersteigt, und wenn die Evaluierung anderer Indikatoren, die eine Bitfehlerrate (Bit Error Rate, BER) des empfangenen optischen Signals, eine detektierte chromatische Dispersion,
eine detektierte Polarisationsmodusdispersion, eine optische Signalleistung des empfangenen
optischen Signals, und/oder einen polarisationsabhängigen Verlust umfassen, die unmittelbar
bevorstehende Faserdurchtrennung in den Lichtleitfaserstrecken (FS) bestätigt.
2. Verfahren nach Anspruch 1,
wobei, wenn eine kritische mechanische Belastung in einer der Lichtleitfaserstrecken
(FS) des Lichtleitfaserlinks (OL) zwischen zwei Netzwerkelementen des optischen Netzwerks
(1) detektiert wird, eine Nachricht oder Benachrichtigung durch den Empfänger gesendet
wird, den Datenverkehr von dem betroffenen Pfad, der die Lichtleitfaserlinks (OL)
mit der betroffenen Lichtleitfaserstrecke (FS) umfasst, fort zu einem Schutzsignalpfad
umzuschalten oder eine Abschaltung des betroffenen Signalpfades, der die Lichtleitfaserlinks
(OL) mit der betroffenen Lichtleitfaserstrecke (FS) umfasst, auszuführen.
3. Verfahren nach Anspruch 1,
wobei eine kritische mechanische Belastung in der betroffenen Lichtleitfaserstrecke
(FS) eines Lichtleitfaserlinks (OL) zwischen zwei Netzwerkelementen des optischen
Netzwerks (1) detektiert wird, wenn eine beobachtete Phasenverschiebung einer Verzögerung
von mehreren Datensymbolen innerhalb eines vorgegebenen Zeitraums äquivalent ist.
4. Verfahren nach einem der vorangehenden Ansprüche 1 bis 3,
wobei das optische Signal durch die Lichtleitfaserstrecken (FS) auf einem Wavelength
Division Multiplexing (WDM)-Kanal transportiert wird.
5. Verfahren nach einem der vorangehenden Ansprüche 1 bis 3,
wobei das optische Signal durch die Lichtleitfaserstrecken (FS) auf einem Optical
Supervisory Channel (OSC) transportiert wird und eine vorgegebene Überwachungswellenlänge
umfasst.
6. Verfahren nach einem der vorangehenden Ansprüche 1 bis 5,
wobei Fälle der überwachten mechanischen Faserbelastung für verschiedene Lichtleitfaserstrecken
(FS) aufgezeichnet und evaluiert werden, um eine betroffene Lichtleitfaserstrecke
(FS) des Lichtleitfaserlinks (OL) zwischen Netzwerkelementen des optischen Netzwerks
(1) zu identifizieren.
7. Verfahren nach Anspruch 6,
wobei die Fälle der überwachten mechanischen Faserbelastung aufgezeichnet werden,
wenn die beobachtete Phasenverschiebung der extrahierten Zeitsteuerungsphase innerhalb
des vorgegebenen Beobachtungszeitraums einen zweiten Schwellenwert übersteigt.
8. Verfahren nach einem der vorangehenden Ansprüche 1 bis 7,
wobei die Zeitsteuerungsphase des empfangenen optischen Signals kontinuierlich überwacht
wird und beobachtete Änderungen der Phasen berichtet werden, um die mechanische Faserbelastung
in den Lichtleitfaserstrecken (FS) des Lichtleitfaserlinks (OL) auf der Basis der
beobachteten Phasenverschiebung abzuleiten.
9. Optisches Netzwerk (1), umfassend:
mehrere Netzwerkelemente (A-F), die über optische Links (OL) miteinander verbunden
sind, die jeweils aus einer oder mehreren Lichtleitfaserstrecken (FS) bestehen;
eine Überwachungseinheit (2A) zum kontinuierlichen Überwachen einer extrahierten Zeitsteuerungsphase
eines empfangenen optischen Signals, das durch Lichtleitfaserstrecken (FS) des optischen
Netzwerks (1) transportiert wird; und
ein Mittel zum Messen einer Phasendifferenz des empfangenen optischen Signals anhand
eines festen Referenzsignals über ein Abtastintervall, um eine Phasenverschiebung
bereitzustellen, die durch eine Zeitdifferenz zwischen dem empfangenen optischen Signal
und dem Referenzsignal repräsentiert wird;
eine Berechnungseinheit (2B) zum Ableiten einer mechanischen Faserbelastung in den
Lichtleitfaserstrecken (FS) auf der Basis einer beobachteten Phasenverschiebung der
extrahierten Zeitsteuerungsphase innerhalb eines vorgegebenen Beobachtungszeitraums;
und
ein Mittel zum Extrahieren der Zeitsteuerungsphase des empfangenen optischen Signals
durch einen Taktwiederherstellungsblock eines Empfängers, der das optische Signal
empfängt, das durch die Lichtleitfaserstrecken (FS) des Lichtleitfaserlinks (OL) transportiert
wird, wobei die Berechnungseinheit (2b) dafür ausgebildet ist, eine kritische mechanische
Faserbelastung zu detektieren, die eine unmittelbar bevorstehende Faserdurchtrennung
anzeigt, wenn die beobachtete Phasenverschiebung der extrahierten Zeitsteuerungsphase
einen ersten Schwellenwert innerhalb des vorgegebenen Beobachtungszeitraums übersteigt,
und wenn die Evaluierung anderer Indikatoren, die eine Bitfehlerrate (Bit Error Rate, BER) des empfangenen optischen Signals, eine detektierte chromatische Dispersion,
eine detektierte Polarisationsmodusdispersion, eine optische Signalleistung des empfangenen
optischen Signals, und/oder einen polarisationsabhängigen Verlust umfassen, die unmittelbar
bevorstehende Faserdurchtrennung in den Lichtleitfaserstrecken (FS) bestätigt.
10. Optisches Netzwerk nach Anspruch 9,
wobei die optischen Links (OL) Lichtleitfaserstrecken (FS) umfassen, die über optische
Verstärker (Optical Amplifiers, OA) in Reihe miteinander verbunden sind.
11. Optisches Netzwerk nach Anspruch 9 oder 10,
wobei das überwachte optische Signal ein optisches Signal ist, das durch die Lichtleitfaserstrecken
(FS) auf einem Wavelength Division Multiplexing (WDM)-Kanal transportiert wird, oder
wobei das überwachte optische Signal ein spezifisches optisches Signal ist, das durch
die Lichtleitfaserstrecken (FS) auf einem Optical Supervisory Channel (OSC) transportiert
wird, und eine vorgegebene Überwachungswellenlänge umfasst.
12. Vorrichtung zum Überwachen einer mechanischen Faserbelastung von Lichtleitfaserstrecken
(FS) eines Lichtleitfaserlinks (OL) innerhalb eines optischen Netzwerks (1), wobei
die Vorrichtung Folgendes umfasst:
eine Überwachungseinheit (2A), die dafür ausgelegt ist, kontinuierlich eine Zeitsteuerungsphase
eines empfangenen optischen Signals zu überwachen, das durch den Lichtleitfaserlink
(OL) transportiert wird, der aus Lichtleitfaserstrecken (FS) zusammengesetzt ist;
ein Mittel zum Messen einer Phasendifferenz des empfangenen optischen Signals anhand
eines festen Referenzsignals über ein Abtastintervall, um eine Phasenverschiebung
bereitzustellen, die durch eine Zeitdifferenz zwischen dem empfangenen optischen Signal
und dem Referenzsignal repräsentiert wird;
eine Berechnungseinheit (2B), die dafür ausgelegt ist, eine mechanische Faserbelastung
in den Lichtleitfaserstrecken (FS) des Lichtleitfaserlinks (OL) auf der Basis einer
beobachteten Phasenverschiebung der Zeitsteuerungsphase innerhalb eines vorgegebenen
Beobachtungszeitraums zu detektieren; und
ein Mittel zum Extrahieren der Zeitsteuerungsphase des empfangenen optischen Signals
durch einen Taktwiederherstellungsblock eines Empfängers, der das optische Signal
empfängt, das durch die Lichtleitfaserstrecken (FS) des Lichtleitfaserlinks (OL) transportiert
wird, wobei die Berechnungseinheit (2b) dafür ausgebildet ist, eine kritische mechanische
Faserbelastung zu detektieren, die eine unmittelbar bevorstehende Faserdurchtrennung
anzeigt, wenn die beobachtete Phasenverschiebung der extrahierten Zeitsteuerungsphase
einen ersten Schwellenwert innerhalb des vorgegebenen Beobachtungszeitraums übersteigt,
und wenn die Evaluierung anderer Indikatoren, die eine Bitfehlerrate (Bit Error Rate, BER) des empfangenen optischen Signals, eine detektierte chromatische Dispersion,
eine detektierte Polarisationsmodusdispersion, eine optische Signalleistung des empfangenen
optischen Signals, und/oder einen polarisationsabhängigen Verlust umfassen, die unmittelbar
bevorstehende Faserdurchtrennung in den Lichtleitfaserstrecken (FS) bestätigt.
1. Procédé de surveillance de contrainte mécanique de fibres de tronçons de fibres optiques
(FS) d'une liaison par fibres optiques au sein d'un réseau optique (1), comprenant
les étapes suivantes :
surveiller en continu une phase de rythme d'un signal optique reçu, transporté au
moyen d'une liaison par fibres optiques (OL) composée de tronçons de fibres optiques
(FS) ;
déterminer la contrainte mécanique de fibres dans lesdits tronçons de fibres optiques
(FS) de ladite liaison par fibres optiques (OL) sur la base d'un déphasage observé
de ladite phase de rythme au sein d'une période de temps prédéterminée d'observation,
dans lequel une différence de phase dudit signal optique reçu est mesurée par rapport
à un signal de référence fixe sur un intervalle d'échantillonnage pour obtenir un
déphasage représenté par une différence de temps entre le signal optique reçu et le
signal de référence, et dans lequel la phase de rythme du signal optique reçu est
extraite par un bloc de récupération d'horloge d'un récepteur recevant ledit signal
optique transporté le long des tronçons de fibres optiques (FS) de ladite liaison
par fibres optiques (OL), dans lequel une contrainte mécanique critique de fibres
indiquant une rupture imminente de fibres est détectée si le déphasage observé de
ladite phase de rythme extraite dépasse une première valeur de seuil, au sein de la
période de temps prédéterminée d'observation, et si l'évaluation d'autres indicateurs
comprenant un taux d'erreur sur les bits, BER (bit error rate), du signal optique reçu, une dispersion chromatique détectée, une dispersion modale
de polarisation détectée, une puissance de signal optique du signal optique reçu,
et/ou une variation de l'affaiblissement en fonction de la polarisation confirme la
rupture imminente de fibres dans les tronçons de fibres optiques (FS).
2. Procédé selon la revendication 1,
dans lequel si une contrainte mécanique critique dans l'un des tronçons de fibres
optiques (FS) de ladite liaison par fibres optiques (OL) entre deux éléments de réseau
dudit réseau optique (1) est détectée, un message ou une notification est envoyé(e)
par ledit récepteur pour commuter le trafic de données hors du trajet affecté comprenant
la liaison par fibres optiques (OL) comportant le tronçon de fibres optiques affecté
(FS) vers un trajet de protection de signaux ou pour effectuer une fermeture du trajet
de signaux affecté comprenant la liaison par fibres optiques (OL) comportant le tronçon
de fibres optiques affecté (FS).
3. Procédé selon la revendication 1,
dans lequel une contrainte mécanique critique dans le tronçon de fibres optiques affecté
(FS) d'une liaison par fibres optiques (OL) entre deux éléments de réseau dudit réseau
optique (1) est détectée si un déphasage observé équivaut à un retard de plusieurs
symboles de données au sein d'une période prédéterminée.
4. Procédé selon l'une des revendications 1 à 3 précédentes,
dans lequel le signal optique est transporté le long desdits tronçons de fibres optiques
(FS) dans un canal de multiplexage par répartition en longueur d'onde, WDM (wavelength division multiplexing).
5. Procédé selon l'une des revendications 1 à 3 précédentes,
dans lequel le signal optique est transporté le long desdits tronçons de fibres optiques
(FS) dans un canal optique de supervision, OSC (optical supervisory channel), et comprend une longueur d'onde de surveillance prédéterminée.
6. Procédé selon l'une des revendications 1 à 5 précédentes,
dans lequel des cas de contrainte mécanique de fibres surveillée de différents tronçons
de fibres optiques (FS) sont enregistrés et évalués pour identifier un tronçon de
fibres optiques affecté (FS) de ladite liaison de fibres optiques (OL) entre des éléments
de réseau dudit réseau optique (1).
7. Procédé selon la revendication 6,
dans lequel les cas de contrainte mécanique de fibres surveillée sont enregistrés
si le déphasage observé de la phase de rythme extraite au sein de la période de temps
prédéterminée d'observation dépasse une seconde valeur de seuil.
8. Procédé selon l'une des revendications 1 à 7 précédentes,
dans lequel la phase de rythme dudit signal optique reçu est surveillée en continu
et des variations observées des phases sont rapportées pour déterminer la contrainte
mécanique de fibres dans les tronçons de fibres optiques (FS) de ladite liaison par
fibres optiques (OL) sur la base du déphasage observé.
9. Réseau optique (1) comprenant :
une pluralité d'éléments de réseau (A à F) connectés les uns aux autres par le biais
de liaisons optiques (OL) composées chacune d'un ou de plusieurs tronçon(s) de fibres
optiques (FS) ;
une unité de surveillance (2A) permettant de surveiller en continu une phase de rythme
extraite d'un signal optique reçu, transporté le long de tronçons de fibres optiques
(FS) dudit réseau optique (1) ; et
un moyen permettant de mesurer une différence de phase dudit signal optique reçu,
par rapport à un signal de référence fixe sur un intervalle d'échantillonnage pour
obtenir un déphasage représenté par une différence de temps entre le signal optique
reçu et le signal de référence ;
une unité de calcul (2B) permettant de déterminer une contrainte mécanique de fibres
dans lesdits tronçons de fibres optiques (FS) sur la base d'un déphasage observé de
ladite phase de rythme extraite, au sein d'une période de temps prédéterminée d'observation
; et
un moyen permettant d'extraire la phase de rythme du signal optique reçu, à l'aide
d'un bloc de récupération d'horloge d'un récepteur recevant ledit signal optique transporté
le long des tronçons de fibres optiques (FS) de ladite liaison par fibres optiques
(OL),
dans lequel l'unité de calcul (2b) est conçue pour détecter une contrainte mécanique
critique de fibres indiquant une rupture imminente de fibres, si le déphasage observé
de ladite phase de rythme extraite dépasse une première valeur de seuil, au sein de
la période de temps prédéterminée d'observation, et si l'évaluation d'autres indicateurs
comprenant un taux d'erreur sur les bits, BER, du signal optique reçu, une dispersion
chromatique détectée, une dispersion modale de polarisation détectée, une puissance
de signal optique du signal optique reçu, et/ou une variation de l'affaiblissement
en fonction de la polarisation confirme la rupture imminente de fibres dans les tronçons
de fibres optiques (FS).
10. Réseau optique selon la revendication 9,
dans lequel les liaisons optiques (OL) comprennent des tronçons de fibres optiques
(FS) connectés les uns aux autres en série par le biais d'amplificateurs optiques
(OA).
11. Réseau optique selon la revendication 9 ou 10,
dans lequel le signal optique surveillé est un signal optique qui est transporté le
long desdits tronçons de fibres optiques (FS) dans un canal de multiplexage par répartition
en longueur d'onde, WDM, ou dans lequel le signal optique surveillé est un signal
optique spécifique transporté le long desdits tronçons de fibres optiques (FS) dans
un canal optique de supervision, OSC, et comprend une longueur d'onde de surveillance
prédéterminée.
12. Appareil de surveillance de contrainte mécanique de fibres de tronçons de fibres optiques
(FS) d'une liaison par fibres optiques (OL) au sein d'un réseau optique (1), ledit
appareil comprenant :
une unité de surveillance (2A) conçue pour surveiller en continu une phase de rythme
d'un signal optique reçu, transporté au moyen de ladite liaison par fibres optiques
(OL) composée de tronçons de fibres optiques (FS) ;
un moyen permettant de mesurer une différence de phase dudit signal optique reçu,
par rapport à un signal de référence fixe sur un intervalle d'échantillonnage pour
obtenir un déphasage représenté par une différence de temps entre le signal optique
reçu et le signal de référence ;
une unité de calcul (2B) conçue pour détecter une contrainte mécanique de fibres dans
lesdits tronçons de fibres optiques (FS) de ladite liaison par fibres optiques (OL)
sur la base d'un déphasage observé de ladite phase de rythme au sein d'une période
de temps prédéterminée d'observation ; et
un moyen permettant d'extraire la phase de rythme du signal optique reçu, à l'aide
d'un bloc de récupération d'horloge d'un récepteur recevant ledit signal optique transporté
le long des tronçons de fibres optiques (FS) de ladite liaison par fibres optiques
(OL), dans lequel l'unité de calcul (2b) est conçue pour détecter une contrainte mécanique
critique de fibres indiquant une rupture imminente de fibres, si le déphasage observé
de ladite phase de rythme extraite dépasse une première valeur de seuil, au sein de
la période de temps prédéterminée d'observation, et si l'évaluation d'autres indicateurs
comprenant un taux d'erreur sur les bits, BER, du signal optique reçu, une dispersion
chromatique détectée, une dispersion modale de polarisation détectée, une puissance
de signal optique du signal optique reçu, et/ou une variation de l'affaiblissement
en fonction de la polarisation confirme la rupture imminente de fibres dans les tronçons
de fibres optiques (FS).